1. Field of the Invention
The invention relates to caulking guns and to dispensing cartridges, and more particularly to the type of composition dispensers in which a cartridge is placed into a so-called caulking gun and a piston urges a plunger forwardly from the rear of the cartridge, thus reducing a volume available for the composition inside the cartridge and forcing the composition from an open tip at the front of the cartridge. These types of caulking guns have been the subject of undesirable afterflow, i.e. the interior of the cartridge is still subject to overpressure after the plunger is no longer actively urged forward and, as a result, additional amounts of composition are forced from the cartridge.
Two primary reasons for the afterflow phenomenon are recognized. Firstly, the usually thin-walled cartridge expands during the plunger actuation and, according to the physical law that systems always attempt to return to the relaxed state, the cartridge wall relaxes after the plunger actuation. Due to the fact that prior art backwalls of the cartridges have been devised to retain their forward-most position and that the plunger of the caulking gun is typically locked against a return movement, the relaxation of the cartridge wall leads to afterflow, i.e. to oozing at the dispensing tip. Secondly, most caulking compositions have a high degree of viscosity and are at least marginally compressible, which, upon plunger actuation, causes a substantial internal pressure buildup which, after the plunger is no longer forced forward, also leads to oozing at the dispensing tip.
The prior art systems are subject to a further drawback. Due to the generally flat design of the cartridge backwall and the rounded, oblique, and nozzle-shaped forward tip of the cartridge, a certain amount of caulking composition remains in the cartridge even after the backwall has reached its forward-most position. The caulking cartridge is thus usually disposed of with a considerable amount of composition still in the cartridge.
2. Description of the Related Art
The afore-described afterflow problem is often answered in the context of conventional prior art structures by quickly releasing and moving back the gun plunger as soon a sufficient amount of composition has been dispensed.
My above-mentioned U.S. Pat. Nos. 5,582,331; 5,704,518; and 5,934,506 disclose a system in which the afterflow problem is largely solved. The outer diameter of the backwall is adjusted relative to the inner diameter of the cartridge such that the backwall will readily move back when the plunger no longer pushes the backwall forward towards the dispensing tip. As will be seen from the following description, I have further improved the invention based on the originally disclosed principles.
U.S. Pat. No. 5,236,105 to Galex describes an older system for preventing over-ejection. There, conventional caulking guns are retrofitted with several members, namely a female element, male element, a return spring, and a stop. The spring is utilized as an active bias sing element which actively pulls back the backwall in the cartridge and thus introduces a relative vacuum inside the cartridge.
U.S. Pat. No. 4,834,268 to Keller describes a plunger system in which an elastic sealing ring is urged towards the inner wall surface of the cartridge by a radial component of the force which urged to plunger forwardly in the dispensing mode. When the plunger is no longer actuated, the sealing ring relaxes slightly and allows the plunger to relax the inside cartridge pressure.
My earlier disclosures and all of the prior art patents have in common that a considerable amount of caulking composition remains in the caulking cartridge after the backwall has reached is forward-most position. In other words, even after the caulking cartridge is xe2x80x9ccompletely spent,xe2x80x9d the cartridge still contains a considerable amount of caulking composition and the cartridge is typically disposed of with an unnecessary amount of caulking composition. Not only does this cause unnecessary waste, but it also unnecessarily burdens the environment.
It is accordingly an object of the invention to provide a caulking cartridge with afterflow prevention and improved purging of cartridge content, which overcomes the above-mentioned disadvantages of the prior art devices and methods of this general type. The primary objects are to provide a simple and inexpensive system which safely prevents overflow or over-ejection and which enables virtually complete purging of the cartridge contents in regular use.
With the foregoing and other objects in view there is provided, in accordance with the invention, an improved caulking cartridge, of the type having a substantially tubular body with a wall having an inner wall surface, a forward dispensing opening at a forward end of the tubular body, a backwall movably disposed within the tubular body, and the tubular body defining a chamber therein bounded by the inner wall surface, the forward end and the backwall, for storing therein a composition to be dispensed through the forward dispensing opening. The improvement comprises:
the backwall having a shape substantially complementary to a shape of the forward end of the tubular body for substantially completely purging the composition from the tubular body when the backwall is pushed against the forward end.
In accordance with an added feature of the invention, the backwall is formed with a nipple substantially equal in size and shape to the forward dispensing opening for driving the composition from the forward dispensing opening when the backwall is pushed against the forward end of the tubular body.
In accordance with an additional feature of the invention, the inner wall surface defines an inner diameter of the tubular body, and wherein the backwall has an outer diameter adapted to the inner diameter of the tubular body such that the composition is allowed to flow into an annular space formed between the inner wall surface and a periphery of the backwall, whereby the backwall moves backwardly away from the forward end of the tubular body when a pressure inside the chamber is greater than a pressure outside the chamber.
In accordance with another feature of the invention, the backwall is formed with a skirt pointing backwardly away from the backwall.
In accordance with a further feature of the invention, the inner wall surface defines an inner diameter of the tubular body, the backwall has an outer diameter substantially equal to the inner diameter of the tubular body, and the skirt has an outer diameter less than the inner diameter of the tubular body.
In accordance with again an added feature of the invention, the skirt is formed with a spacer ring at an end thereof distal from the backwall.
In accordance with an alternative feature of the invention, the skirt is formed with a plurality of spacer tabs at an end thereof distal from the backwall. In this case, it is possible to form the skirt is a plurality of tab strips extending from the backwall to the spacer tabs.
With the above and other objects in view there is provided a further improvement, namely:
the backwall having a skirt formed thereon pointing backwardly away from the backwall and being formed with a stop surface distally from the backwall;
the skirt having an outer diameter less than the inner diameter of the tubular body and forming a space between the skirt and the inner wall surface;
a sealing ring disposed in the space between the skirt and the inner wall surface and sealing against the inner wall surface, the sealing ring having an axial width less than a spacing distance between the stop surface and the backwall.
In accordance with again an additional feature of the invention, the backwall has an outer diameter substantially equal to the inner diameter of the tubular body.
In accordance with again a further feature of the invention, the stop surface may be formed on the spacer ring or the individual spacer tabs.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a caulking cartridge with afterflow prevention and improved content purging, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of the specific embodiment when read in connection with the accompanying drawings.